The invention relates generally to implantable drug delivery systems and, particularly, to an implantable pump having a controller regulating the delivery of the drug.
Implantable drug delivery systems infuse drugs to tissue treatment sites inside of patients. For example, morphine is delivered to a spinal cord region by implanted drug delivery systems to provide long term pain relief to patients suffering chronic pain. Conventional wisdom teaches that drugs for chronic pain are to be infused at a continual rate to provide uniform and steady drug delivery to the treatment sites. Accordingly, implantable drug delivery systems are programmed or otherwise configured to deliver drug in a constant flow fashion.
However, granuloma can arise around the catheters associated with implanted drug delivery systems. Granuloma formation is typically an inflammatory tissue mass that forms around the catheter. A granuloma formation near a spinal cord may press on the cord and cause neurological side-effects. Catheters to deliver morphine are typically positioned near the spinal cord in patients. There is a need to reduce the risk of granuloma formation associated with implantable morphine drug delivery systems.
Granuloma formation at catheter tips is discussed in Deer et al, “Management of Intrathecal Catheter-Tip Inflammatory Masses: An Updated 2007 Consensus Statement From An Expert Panel” (Neuromodulation: Technology at the Neural Interface, Vol. 11, No. 2, 2008) (“Deer Article”) which reports the results of an expert panel that considered granulomas caused by intrathecal (IT) therapies, where IT refers to injections into the spinal canal. The Deer Article at page 86 states that “granulomas are most likely a function of drug dose, drug concentrations, a combination of the two, the way the drug is delivered and/or CSF [cerebrospinal fluid] flow rate.” Also, the Deer Article at page 86 reports that “[m]ost panelists thought that there does exist a difference, theoretically at least, in the rate of granuloma formation caused by bolus infusion vs. continuous infusions through the catheter . . . . However, the panel did also feel that frequent repeated boluses of high-concentration opioid medications might potentially lead to a similar proinflammatory effect as continuous infusions.” Further, the Deer Article at page 87 reports that consideration as given to prophylactic measures that might prevent granulomas including “using bolus dosing instead of slow continuous infusion, minimizing concentration/dose of the agent infused (e.g., especially of morphine sulfate and hydromorphone) to the daily dose limits proposed by the Consensus Panel, avoiding ultra slow flow rates and/or delivering the drug into larger CSF space over the spinal cord.”
The recommendations for preventing granuloma formation stated in the Deer Article at page 89 include: “minimize concentrations and doses of intrathecal (IT) agents, especially of morphine sulfate and hydromorphone” and “avoid ultra-slow flow rates.” The reported recommendations do not include intermittent bolus drug delivery.